This invention relates to high pressure gasification of carbon-containing fuels, e.g., coal, with oxygen and steam, and in particular to a process wherein the oxygen is produced in an air separation plant and the steam is formed in a gas-heated steam generator, e.g., a boiler, and the waste gases produced in the steam boiler are subsequently expanded in an expansion turbine.
In conventional high pressure gasification processes, either air or oxygen-enriched air is utilized in addition to the steam. (For details of such processes, attention is directed to the comprehensive literature, for example, Riegel's Handbook of Industrial Chemistry, 7th edition, Ed. J. A. Kent, Van Nostrand Reinhold Company, New York, 1974, pp. 44-54 and references cited on p. 61, especially von Fredersdorff, C. G. and Elliott, M. A., "Coal Gasification. Chemistry of Coal Utilization", Suppl. Vol., H. H. Lowry Ed., pp. 892-1022, New York, John Wiley and Son, 1963.) The heating value of the fuel gas formed by high pressure gasification increases in proportion to the oxygen content of the oxygen-containing stream. For this reason, in order to produce a fuel gas having a high heating value, an air separation plant is employed to produce a highly enriched oxygen stream.
To provide the heat necessary for steam generation, either coal or, in the present case, part of the fuel gas product is burned with air. The resultant combustion gases (hereinafter termed "waste gases"), which are still under pressure, are subsequently expanded to recover the compression energy contained therein.
The steam boiler and the air separation plant are conventionally operated in parallel and substantially independently of each other. In such processes, however, it has heretofore been impossible to attain an entirely satisfactory energy balance.